Study on bycatch of cetaceans by purse seine fishery in the Western and Central Pacific Ocean

Increasing attention has been paid to fisheries interactions with cetacean populations, however the magnitude of cetacean interaction with fisheries is still poorly known. A quantitative analysis of cetacean bycatch in tuna purse seine fishery was conducted based on fishery and bycatch data released by the Secretariat of the Western and Central Pacific Fisheries Commission from 2013 to 2020. The results showed that a total of 9 881 cetaceans classified as 30 species interacted with purse seine fishery. The annual bycatch rate ranged from 1.781 per hundred sets to 4.214 per hundred sets. The interactions were mainly distributed in the waters around Papua New Guinea, Solomon Islands, Micronesia, Marshall Islands, Nauru, Kiribati, and Tuvalu (10°S-5°N, 130°E-180°W). The main cetaceans that interacted frequently with purse seine were false killer whales (Pseudorca crassidens), rough-toothed dolphins (Steno bredanensis), short-finned pilot whales (Globicephala macrorhynchus), bottlenose dolphins (Tursiops truncatus), spinner dolphins (Stenella longirostris), Bryde’s whales (Balaenoptera edeni), sei whales (B. borealis) and Indo-Pacific bottlenose dolphins (T. aduncus), of which the rough-toothed dolphins and bottlenose dolphins were vulnerable to purse seine. In addition, there were significant differences (P<0.05) in bycatch and net bycatch rates between odontoceti and mysticeti. Furthermore, the bycatch rates of bottlenose dolphins, short-finned pilot whales and sei whales were positively correlated with tuna catch rates. On the contrary, the bycatch rates of sperm whales (Physeter macrocephalus) and Risso’s dolphins (Grampus griseus) were negatively correlated with tuna catch rates. We suggested that in the management of tuna purse seine fisheries, training for crew’s ability to increase the understanding of cetacean habitat and life history should be strengthened. The results of this study may improve our understanding of cetacean bycatch and facilitate to develop more adequate mitigation measure for cetaceans in the Western and Central Pacific Ocean.